Vol.:(0123456789) 1 3 International Journal of Environmental Science and Technology https://doi.org/10.1007/s13762-019-02548-4 ORIGINAL PAPER Continuous decolorization of dye solution by homogeneous Fenton process in a rotating packed bed reactor J. B. Modak 1  · A. Bhowal 1  · S. Datta 1  · S. Karmakar 1 Received: 8 May 2019 / Revised: 28 August 2019 / Accepted: 23 September 2019 © Islamic Azad University (IAU) 2019 Abstract Continuous decolorization of Methyl Orange solution by homogeneous Fenton reaction was studied in a rotating packed bed reactor to intensify micromixing. In this equipment, the reactants fowed radially outward under centrifugal acceleration between a pair of rotating cylindrical disk packed with glass beads. The magnitude of the pseudo-frst-order kinetic constant estimated from the experimental data was noted to increase with rotational speed and bed depth but did not signifcantly change with solution fow rate. It varied between 1.7 and 72 s −1 for the experimental conditions studied. The constant was over two orders of magnitude higher in rotating packed bed in comparison with conventional continuous stirred tank and packed bed reactors. Steady state was achieved in a much shorter time period in the former. The study also indicated that decolorization of a given volume of dye solution can be done at a faster rate by continuously recirculating the same volume of solution through rotating packed bed than in a mechanically agitated batch reactor. Keywords Centrifugal acceleration · Homogeneous Fenton process · Methyl Orange · Pseudo-reaction rate constant Introduction Large quantities of dye-containing wastewater are generated during the manufacturing and processing of textile industry products (Fu et al. 2010). Azo dyes contribute to about 70% of all used dyes. The color of these dyes is due to azo bond and associated chromophores (Thiam et al. 2015). Disposal of dyes into surface water not only afects the aesthetic but also have a deleterious efect on the ecosystem as they are toxic to aquatic life and human being (Monash and Pugaz- henthi 2009). Advanced oxidation process (AOP) is a promising alter- native for decolorizing efuent, where conventional waste water treatment processes (biological, physical and chemi- cal) have low removal efciency, or is inefective (Bokare and Choi 2014). This technique involves oxidation of organic compounds present in water into products like CO 2 , H 2 O and/or inorganic salts by hydroxyl radicals. Fenton process is one of the oldest AOP (Wu et al. 2008). It uses ferrous salt as the catalyst and hydrogen peroxide as an oxidizing agent to generate hydroxyl radicals through the following reaction: The hydroxyl radical attacks the dye molecule and causes cleavage of the azo bond (N=N). This leads to degradation of the dye and decolorization of the solution (Elmorsi et al. 2010). Ferrous ions are regenerated through reduction of ferric ions with hydrogen peroxide: Typically homogeneous Fenton process has been studied in batch system (Krüger et al. 2009; Ramirez et al. 2009). Continuous operation has been reported in a continuous stirred tank reactor (CSTR) and fuidized bed reactor. Zhang et al. (2006) and Kong and Lemley (2006) investigated the efect of operating parameters on the efcacy of Fenton pro- cess with landfll leachate and carbaryl as the target pollut- ants, respectively, in a CSTR. The performance of fuidized- bed Fenton process was evaluated by Su et al. (2011) for the decolorization and oxidation of textile wastewater. Anotai et al. (2012) determined the optimal conditions for the deg- radation of ethanolamine from TFT-LCD wastewater by Fenton process using the same contactor. (1) Fe 2+ + H 2 O 2 → Fe 3+ + ⋅ OH + HO - (2) Fe 3+ + H 2 O 2 → Fe 2+ + ⋅ H 2 O + H + Editorial responsibility: Q. Aguilar-Virgen. * A. Bhowal avijit.bhowal05@gmail.com 1 Department of Chemical Engineering, Jadavpur University, Kolkata 700032, India